The invention relates to an improved method for the thermoremanent duplication of magnetic tapes using radiant heating and contact cooling with applied pressure, controlled tension, and precision tape guidance.
Currently, the videotape industry duplicates videotapes at substantial expense by using many copiers to electronically reproduce from a master tape at normal slow playback speed. The master tape is run in real time while up to 1000 copiers in one room record the information. A need exists for a reproduction method which is faster and less costly.
Magnetic tapes have been previously reproduced by anhysteretic contact printing in which the master tape and the copy are placed in face to face contact and exposed to a decaying a.c. magnetic field. (Herr et al. U.S. Pat. No. 2,738,383). Reproduction by this means, however, requires high coercivity master tapes and transfers signals weaker than those present in the master.
Also previously proposed has been a method of duplication involving thermoremanent transfer wherein the blank copy magnetic tape is heated above its Curie point and thereafter cooled in intimate contact with the prerecorded master tape whereby the signals of the master are transferred to the copy tape. (Greiner et al. U.S. Pat. No. Re 28,290; Daly et al. U.S. Pat. No. 3,612,102; Hoell U.S. Pat. No. 3,699,267; Lemke U.S. Pat. No. 3,541,577; Kumada U.S. Pat. No. 3,465,105, Kobayashi et al. U.S. Pat. No. 3,824,617.)
Thermoremanent reproduction has the advantage that the copied magnetic recording may have an even greater intensity of signal than that of the original. However disadvantages in previous thermal remanent copying systems have included (1) overheating of the base film resulting in physical distortions which produce electronic timing errors during playback and (2) high frequency roll-off, that is the loss in transfer of high frequencies, due to the inadequate contact pressure between master and copy.
One attempt to control overheating of the base film and prevent high frequency roll-off has been using a finely focussed laser beam to provide rapid localized heating of the copy tape magnetizable particles to a temperature above their Curie point. The laser spot size is approximately 5 .mu.m commensurate with the magnetic particle size. A scanning laser beam to cover the entire tape width is required (Stancel U.S. Pat. No. 3,761,645).